Once you get a feel for this tight’s soft, lightweight comfort, you’ll never start a cold-weather mission without it. The foundation is our signature PeakWool™ Lightweight fabric, a single-knit blend that combines the moisture wicking, odor management and thermal regulation of merino wool with the softness, durability and stretch of synthetic fibers. Flatlock seams and a smooth, low-profile waistband minimize chafing and slide easily under your outer layer of choice.